(1) Field of the Invention
The present invention relates to a storage container for precision substrates which is used in accommodating, storing, preserving, conveying and shipping precision substrates such as semiconductor wafers, lead frames, mask glass substrates, etc., and which is mounted in position with regard to diverse, automatic machines as well as relating a positioning mechanism therefor and to a method of positioning the storage container for precision substrates.
(2) Description of the Prior Art
For development of semiconductor chips into large-sized configurations and increase in productivity therefor, an international agreement as to large-diametric semiconductor wafers (to be referred to simply as wafers hereinbelow) was recently established. This agreement has promoted a variety of earnest study and research of semiconductor manufacturing equipment and systems and has been followed by their development. Because of this, a variety of studies and development into storage containers for precision substrates for storing and shipping wafers have been made in order to improve their durability, sealing performance, good anti-staining performance, unmanned use, automation, ease of cleaning, etc. This storage container for precision substrates will be hereinbelow described with reference to a typical case where wafers are to be contained.
In a case shown in FIG. 1, a storage container for precision substrates of this type is mainly composed of a container body 1 having a open front face 2 opening to the front, forming a front-open box configuration. A pair of aligning plates 21 having a plurality of aligning ribs 3A are attached to the interior side walls of this container body 1 using screw type fasteners. These paired aligning plates 21 horizontally support a multiple number of wafers W in alignment with their aligning ribs 3A. In other cases shown in FIGS. 2 and 3, a plurality of aligning ribs 3A are integrally molded with the interior side walls of a container body 1, arranged vertically.
Generally, a wafer W is thin and brittle and also it has an extremely low tolerance to micro-dust pollution. Therefore, during accommodating, storage, preservation, conveyance and shipping of wafers W or in the factory and while handling them during the production process, it is preferred that the wafers are kept in a clean environment free from dust and staining from sources such as the factory workers and that they are handled by an unmanned or automatic process using various automatic machines (see FIG. 3) 12 such as an unloader, automatic wafer transporting device etc. To realize handling by these automatic machines 12 while enabling high speed access (the time required for positioning correction of container body 1 and transfer is 40 seconds or less, or preferably 20 seconds or less) to improve the productivity of the semiconductor manufacturing, it is important to load the storage container for precision substrates onto a stage 13 in automatic machine 12 using a positioning means and thereby highly, precisely, position container body 1 and multiple aligning ribs 3A into a normalized position.
This positioning means can typically be made up of a mateable configuration. Illustratively, a plurality of concave members, e.g., positioning members 22 having concavities on their surface are provided on the undersurface of container body 1 while corresponding projections, that is, projected member or positioning pins 14 (to be referred to as projected members) as projected members are provided at the corresponding positions on stage 13 of automatic machine 12 so that these multiple concave members fit on positioning pins 14 to thereby precisely position and mount the storage container for precision substrates onto stage 13 in automatic machine 12.
As a specific method of providing the concave members on container body 1, a plurality of positioning members 22 (three in FIG. 1) are provided on positioning plate 23, as shown in FIG. 1, which in turn is attached to the undersurface of container body 1 using adhesive or fasteners. As another specific method, positioning members 22 may be attached directly to the undersurface of container body 1 without use of a positioning plate, as shown in FIG. 2.
There is another method shown in FIG. 3. In this case, a plurality of solid projections 24 which each extend further by at least 10 mm or more, on either side, from the external diameter of positioning pin 14 are formed integrally with the undersurface of the container body by injection molding. The distal end of each projection 24 is formed with a concave face so that the projection is sectionally configured in an inverted V-shape. The center of this concave bottom is used as a positioning concavity 8A while the slanting surfaces on both sides defining concavity 8A are used as guide surfaces 11A so that positioning pin 14, if it is displaced, can be fitted into concavity 8A with the help of these guide surfaces 11A. Here, in FIG. 3, a gap is shown between positioning pin 14 and concavity 8A, this is just for convenience sake to depict the structure, and positioning pin 14 of course abuts concavity 8A in an actual case.
Prior art relating to storage containers for precision substrates of this type has been disclosed in Japanese Utility Model applications Laid-Open Sho 63 No. 82,788 and Sho 63 No. 166,948 and Japanese Patent Application Laid-Open Hei 9 No. 107,025.
Since the concave members are provided for container body 1 in a manner described above, the storage container for precision substrates has suffered from various problems as follows:
First, when the concave members are attached to container body 1 by using, or without using, positioning plates 23 as separate parts, positioning plates 23 and/or concave members are attached using adhesive or fasteners. Therefore, an error more than .+-.0.2 mm arises when it is assembled or attached, producing difficulties in keeping it in position. This causes a risk of damage to wafers W when wafers W are taken in or out with respect to automatic machine 12.
Further, since guide surfaces 11A which perform guidance functions are also injection molded at the same time as container body 1 and projections 24 are integrally formed by injection molding, shrinkage, i.e., warpage or distortion occurs at projections 24 and thereabout due to molding shrinkage because the thickness of the container at projections 24 locally becomes much greater about five times as great as that of the other part of container body 1. Therefore, it is impossible to expect the dimensions to fall within a precision range within .+-.0.2 mm. In order to eliminate this problem, the parting joints in the mold may be shaped so as to avoid projections 24. However, this makes it difficult to release the container body from the mold, needs a complicated mold configuration and increases the number of mold parts and degrades the productivity. Moreover, when guide surfaces 11A are integrally formed by injection molding, it is no longer possible to change the length, angle and other dimensions of guide surfaces 11A after injection molding. Therefore, the resulting product can only be handled by automatic machines 12 of identical specifications, having no flexibility in its use.